System and method for energy savings on a phy/mac interface for energy efficient ethernet

ABSTRACT

A system and method for energy savings on a PHY/MAC interface for energy efficient Ethernet. Power savings for a PHY due to low-link utilization can also be realized in the higher layer elements that interface with the PHY. In one embodiment, subrating is implemented on a MAC/PHY interface to match a subrating of the PHY with a remote link partner. This subrating is less than the full capacity rate and can be zero.

This application claims priority to provisional application No.61/028,179, filed Feb. 12, 2008, which is incorporated by referenceherein, in its entirety, for all purposes.

BACKGROUND

1. Field of the Invention

The present invention relates generally to Ethernet systems and, moreparticularly, to a system and method for energy savings on a physicallayer device (PHY)/media access control (MAC) interface for energyefficient Ethernet.

2. Introduction

Energy costs continue to escalate in a trend that has accelerated inrecent years. Such being the case, various industries have becomeincreasingly sensitive to the impact of those rising costs. One areathat has drawn increasing scrutiny is the IT infrastructure. Manycompanies are now looking at their IT systems' power usage to determinewhether the energy costs can be reduced. For this reason, an industryfocus on energy efficient networks has arisen to address the risingcosts of IT equipment usage as a whole (i.e., PCs, displays, printers,servers, network equipment, etc.).

In designing an energy efficient solution, one of the considerations isthe traffic profile on the network link. For example, many network linksare typically in an idle state between sporadic bursts of data, while inother network links, there can be regular or intermittent low-bandwidthtraffic, with bursts of high-bandwidth traffic. An additionalconsideration for an energy efficient solution is the extent to whichthe traffic is sensitive to buffering and latency. For example, sometraffic patterns (e.g., HPC cluster or high-end 24-hr data center) arevery sensitive to latency such that buffering would be problematic. Forthese and other reasons, applying energy efficient concepts to differenttraffic profiles would lead to different solutions. These variedsolutions can therefore seek to adapt the link, link rate, and layersabove the link to an optimal solution based on various energy costs andimpact on traffic, which itself is dependent on the application.

One example of an EEE solution is a low power idle (LPI) mode. Ingeneral, LPI relies on turning the active channel silent when there isnothing to transmit. When data is transmitted, it is transmitted at fullPHY capacity. Energy is thereby saved when the link is off. Anotherexample of an EEE solution is a subrating technique where the link rateis reduced when the high data capacity is not needed. In the physicallayer, this subrating technique is enabled by the use of a subset of theparent PHY. While these various EEE solutions can provide significantenergy savings, what is needed is a mechanism for saving energy in allinterfaces of the PHY.

BRIEF DESCRIPTION OF THE DRAWINGS

In order to describe the manner in which the above-recited and otheradvantages and features of the invention can be obtained, a moreparticular description of the invention briefly described above will berendered by reference to specific embodiments thereof which areillustrated in the appended drawings. Understanding that these drawingsdepict only typical embodiments of the invention and are not thereforeto be considered limiting of its scope, the invention will be describedand explained with additional specificity and detail through the use ofthe accompanying drawings in which:

FIG. 1 illustrates the ISO Open System Interconnection (OSI) referencemodel and its mapping to the IEEE 802.3 layering.

FIG. 2 illustrates a flowchart of a process of the present invention.

FIG. 3 illustrates an example interface between a MAC and a PHY.

FIGS. 4 and 5 illustrates another view of an example interface between aMAC and a PHY.

SUMMARY

A system and method for energy savings on a PHY/MAC interface for energyefficient Ethernet, substantially as shown in and/or described inconnection with at least one of the figures, as set forth morecompletely in the claims.

DETAILED DESCRIPTION

Various embodiments of the invention are discussed in detail below.While specific implementations are discussed, it should be understoodthat this is done for illustration purposes only. A person skilled inthe relevant art will recognize that other components and configurationsmay be used without parting from the spirit and scope of the invention.

Ethernet has become an increasingly pervasive technology that has beenapplied in various contexts such as twisted pair and backplane. IEEE802.3az Energy Efficient Ethernet (EEE) continues to evaluate variousmethods for reducing energy used by reducing link rates during periodsof low link utilization. In this process, a protocol would be definedthat would facilitate transitions to and from lower power consumptionmodes in response to changes in network demand.

In general, a reduction in link rate to a sub-rate of the main rateenables a reduction in power, thereby leading to energy savings. In oneexample, this sub-rate can be a zero rate, which produces maximum powersavings. In one example, a subset PHY technique can be used to reducethe link rate to a sub-rate. In this subset PHY technique, a low linkutilization period can be accommodated by transitioning the PHY to alower link rate that is enabled by a subset of the parent PHY. In oneembodiment, the subset PHY technique is enabled by turning off portionsof the parent PHY to enable operation at a lower or subset rate. Forexample, a subset 1 G PHY can be created from a parent 10 GBASE-T PHY bya process that turns off three of the four channels. In anotherembodiment, the subset PHY technique is enabled by slowing down theclock rate of a parent PHY. For example, a parent PHY having an enhancedcore that can be slowed down and sped up by a frequency multiple can beslowed down by a factor of 10 during low link utilization, then sped upby a factor of 10 when a burst of data is received. In this example of afactor of 10, a 10 G enhanced core can be transitioned down to a 1 Glink rate when idle, and sped back up to a 10 G link rate when data isto be transmitted. In another example of subrating, a protocol such aslow power idle (LPI) can be used to create a sub-rate of zero. Ingeneral, LPI relies on turning the active channel silent when there isnothing to transmit. Energy is thereby saved when the link is off.

As these examples illustrate, power savings can be realized through theimplementation of subrating by the PHY during periods of low linkutilization. It is a feature of the present invention that power savingscan also be realized beyond the PHY itself during periods of low linkutilization. To illustrate the principles of the present invention,reference is first made to FIG. 1, which illustrates the ISO Open SystemInterconnection (OSI) reference model and its mapping to the IEEE 802.3layering.

As illustrated, the physical layer (often referred to as the PHY)includes a physical coding sublayer (PCS), a physical medium attachment(PMA), physical media dependent (PMD), and auto-negotiation (AN). Itshould be noted that some of these layers (e.g., auto-negotiation) areoptional for some PHY types, and that some PHY types do no use all ofthe sub-layers. As illustrated, the PCS is coupled to a reconciliationsublayer (RS), which provides a signal mapping between interface 110 andthe MAC layer. In various examples, interface 110 can be based on anAttachment Unit Interface (AUI), media independent interface (MII),serial MII (SMII), reduced MII, (RMII), gigabit MII (GMII), reduced GMII(RGMII), serial GMII (SGMII), quad serial gigabit MII (QSGMII), 10gigabit MII (XGMII), SXGMII, XFI, 10-Gbps AUI (XAUI), or the like. In anMII example, the PCS is generally responsible for encoding/decodingto/from five-bit code-groups (4B/5B) for communication with theunderlying PMA. In a GMII example, the PCS is generally responsible forencoding/decoding GMII octets to/from ten-bit code-groups (8B/10B) forcommunication with the underlying PMA. In an XGMII example, the PCS isgenerally responsible for encoding/decoding XGMII 64-bit data to/from66-bit code-groups (64B/66B) for communication with the underlying PMA.In various embodiments, one or more parts of the PHY can be internal orexternal to the MAC. In one embodiment, an extender such as the XAUIextender sublayer (XGXS) or XFI can be used between the MAC/PHY.

In general, the PMA abstracts the PCS from the physical medium.Accordingly, the PCS can be unaware of the type of medium. The primaryfunctions of the PMA include mapping of transmit and receive code-groupsbetween the PCS and PMA, serialization/de-serialization of code-groupsfor transmission/reception on the underlying PMD, recovery of clock fromthe coded data (e.g., 4B/5B, 8B/10B, 64B/66B, etc.) supplied by the PMD,and mapping of transmit and receive bits between the PMA and PMD.

The PMD is generally responsible for generating electrical or opticalsignals depending on the nature of the physical medium connected. PMDsignals are sent to the medium dependent interface (MDI), which is theactual medium connected, including connectors, for the various mediasupported.

As noted, one of the ways of creating an energy efficient network isthrough efficient link utilization. In general, the lack of datatransmission does not significantly reduce energy consumption of a PHYin most implementations. A 10 Gbit/s link, for example, will consumeabout the same amount of power whether a burst of data is transmittedduring a file transfer, a constant stream of data is transmitted atlower bandwidth, or no data is transmitted during an idle period. Ifsubrating is used on a 10 Gbit/s link during idle times, then power canbe saved in the operation of the PHY.

In accordance with the present invention, it is recognized that ifsubrating is used in the PHY, then power savings can also be realized inthe higher layer elements (e.g., MAC layer) that interface with the PHY.In other words, a change in the PHY to produce energy savings cantrigger a change upstream to produce additional energy savings. In oneembodiment, an entry by the PHY into a lower-power consumption mode(e.g., LPI or subset PHY mode) can enable the PHY's MAC interface tosimilarly enter into a lower-power consumption mode. Power savings canthen be realized on the MAC side and PHY side of the interface, as wellas in the interface itself.

To illustrate the principles of the present invention, reference is nowmade to the flowchart of FIG. 2, which illustrates an EEE processbetween two link partners. As illustrated, the process begins at step202 where an EEE control policy indicates the need to transition to alower power consumption mode. As would be appreciated, the EEE controlpolicy can be based on an analysis of various link-related parameters.In the present example, the EEE control policy is implemented in a layerabove the PHY (e.g., MAC), although in an alternative embodiment, theEEE control policy is implemented in the PHY itself to enable legacysupport. As would be appreciated, the particular location of the EEEcontrol policy would be implementation dependent.

At step 204, the needed transition to a lower power consumption mode issignaled by the local MAC to the local PHY. For example, in thesubrating case of LPI, the MAC can assert LPI (rather than regular idle)on the local MAC/PHY interface (e.g., xxMII). After such signaling, thesubrating can be applied to the local MAC/PHY interface at step 206. Forexample, once the LPI command has been given, there is no need for theTX part of the MAC/PHY interface to stay on and both the MAC side aswell as the PHY side can save power by implementing a zero subrating.Here, the PHY side of the TX on the local partner can switch everythingoff in its circuitry that faces that portion of the MAC. To get out ofthis state, the MAC can assert a signal (for example a clock in thexxMII implementation) and the PHY can keep some form of energy detectoralive.

FIG. 3 illustrates an example of a MAC/PHY interface that can implementsubrating. In various embodiments, PCS/PMA 320 and PMD 330 can beimplemented separately or as a single chip. As illustrated, theinterface between MAC 310 and PCS/PMA 320 of the PHY is facilitated byXAUI extender sublayer (XGXS) 212, 222, which further facilitates four3.125 Gb/s transmit/receive channels using 8B/10B encoding. In general,XAUI is a low pin count, self-clocked serial bus that is designed as aninterface extender for XGMII. Here, XAUI provides a mapping betweenXGMII and serial. The four XAUI channels map to the MDI. XAUI may beused in place of (or to extend) XGMII in various chip-to-chipapplications due to reduced pin count and much longer allowed tracelengths. In one application such as backplane Ethernet IEEE 802.3ap,10-Gbit operation can be enabled using the 10 GBASE-KX4 implementation,which specifies four channels (similar to XAUI).

FIG. 4 illustrates another view of the MAC/PHY interface for the exampleof a 10 G link of FIG. 3. As illustrated, the interface between MAC 410and PHY 420 is supported by four separate channels 430 a-430 d. Each ofthese four separate channels 430 a-430 d would be active in operation ata 10 G link rate.

As FIG. 4 further illustrates, an EEE control signal from a controlleris transmitted from the MAC to the PHY to indicate the transition to alower power consumption mode. In one embodiment, the implementation ofsubrating of the MAC/PHY interface in response to the transition to thelower power consumption mode can be effected through the transition ofone or more channels of the MAC/PHY interface into an inactive state.For example, a lower power consumption mode of the MAC/PHY interface canbe effected by having a single channel 430 a active, while the remainingchannels 430 b, 430 c, 430 d are all placed in an inactive state. In oneembodiment, the channels that are shut down can use a low duty cyclesignal that consumes minimal power to ensure that synchronization is notlost.

In the above example, subrating is effected through shutting down one ormore of the channels in the MAC/PHY interface. If a single channel isused in the MAC/PHY interface, then the interface of the single channelcan be slowed down. In yet another scenario, one or more channels in amultiple channel MAC/PHY interface can be slowed down. In general, theMAC/PHY interface can be configured for operation at a rate indicated bythe control signal. In various embodiments, this configuration caninclude the subrating of one or more channels on the MAC/PHY interface,thereby yielding a variable MAC/PHY interface.

Referring again to the flowchart of FIG. 2, the request to transition toa lower power consumption is also translated by the local PHY to thephysical domain on the MDI at step 208. In general, the new link rate ofthe PHY on the MDI can be matched to the slower equivalent rate in thelocal MAC/PHY interface. Here, the subrating of the link rate betweenthe local and remote link partners can be implemented by various PHYtechniques such as LPI, subset PHY, etc.

Next, at step 210, the PHY on the remote side receives the physicalsignaling on its RX on the MDI and initiates going into the lower energyconsumption mode. As would be appreciated, the particular protocol usedwould be implementation dependent. On the remote end of the link, atstep 212, the remote PHY would then inform the remote MAC that it hasreceived a request for lower energy in the RX direction. In a similarmanner to the local MAC/PHY (See FIG. 5), an EEE control signal can betransmitted from remote PHY 510 to remote MAC 520 across the remoteMAC/PHY interface that can comprise one or more channels 530 a-530 d.

Finally, at step 214, after such signaling, subrating can be applied tothe remote MAC/PHY interface. Again, subrating can be effected throughshutting down one or more of channels 530 a-530 d in the MAC/PHYinterface. If a single channel is used in the MAC/PHY interface, thenthe interface of the single channel can be slowed down. In yet anotherscenario, one or more channels 530 a-530 d in the MAC/PHY interface canbe slowed down.

As described in the above example, power savings can be realized throughthe implementation of subrating on an asymmetric link where the entiredirection of transmission between two link partners would transitioninto a lower power consumption mode. Depending on the specific protocolemployed, the remote side of the link can either follow the lead of thelocal side or can block going into the lower power state. In oneembodiment, a symmetric application of subrating can be used in a givenlink between two link partners. As would be appreciated, the specificamount of subrating used during a low power consumption mode would beimplementation dependent.

In FIGS. 4 and 5, the communication of the EEE control signal by acontroller is illustrated as occurring generally across the MAC/PHYinterface. This generic illustration is due to the variousimplementations of the MAC/PHY interface as well as the form ofcommunication. For example, the EEE control signal could be applied toMAC/PHY interfaces that are internal or external. Moreover, the EEEcontrol signal could be enabled using in-band signaling, out-of-bandsignaling, register-based communication, etc. As would be appreciated,the specific form of communication in relation to the MAC/PHY interfacewould be implementation dependent.

As described, it is a feature of the present invention that a transitionin power consumption mode in the PHY can also produce a transition inthe power consumption mode of the MAC/PHY interface. This feature of thepresent invention can be applied to various forms of the internal orexternal MAC/PHY interface, and is not confined to a conventionalxxMII-type interface. For example, an external MAC/PHY interface caninclude one or more extenders that are facilitated by stub chips andsuitable buffering. In this example, the subrating (e.g., LPI, subsetPHY, or other power-savings techniques in the PHY) can be applied to themultiple extenders as well as supporting circuitry.

As would be appreciated, the principles of the present invention can beapplied to various PHY types (e.g., backplane, twisted pair, optical,etc.), standard (e.g., 1 G, 10 G, etc.), non-standard (e.g., 2.5 G, 5 G,etc.), or future link rates (e.g., 40 G, 100 G, etc.), as well asdifferent port types and media types. Further, the principles of thepresent invention can also be applied to the pairing of EEE PHYs withlegacy MACs in implementing subrating on a MAC/PHY interface usinglegacy support techniques.

These and other aspects of the present invention will become apparent tothose skilled in the art by a review of the preceding detaileddescription. Although a number of salient features of the presentinvention have been described above, the invention is capable of otherembodiments and of being practiced and carried out in various ways thatwould be apparent to one of ordinary skill in the art after reading thedisclosed invention, therefore the above description should not beconsidered to be exclusive of these other embodiments. Also, it is to beunderstood that the phraseology and terminology employed herein are forthe purposes of description and should not be regarded as limiting.

1. An energy efficient Ethernet method in a physical layer device,comprising: detecting a need for transitioning of the physical layerdevice between different power consumption modes; and transitioning arate of transmission on an interface between the physical layer deviceand said media access control device from a first rate to a second rate.2. The method of claim 1, wherein said first rate is greater than saidsecond rate.
 3. The method of claim 1, wherein said second rate isgreater than said first rate.
 4. The method of claim 1, wherein saidtransmitting comprises transmitting using in-band signaling.
 5. Themethod of claim 1, wherein said transmitting comprises transmittingusing out-of-band signaling.
 6. The method of claim 1, wherein saidtransmitting comprises transmitting using register-based communication.7. The method of claim 1, wherein said transitioning comprisesinactivating one or more channels in said interface.
 8. The method ofclaim 1, wherein said transitioning comprises reducing a rate oftransmission on one or more channels in said interface.
 9. The method ofclaim 1, further comprising transmitting a control signal to the mediaaccess control device for said transitioning.
 10. The method of claim 1,further comprising receiving a control signal from the media accesscontrol device for said transitioning.
 11. An energy efficient Ethernetmethod, comprising: operating a physical layer device in an active powermode; transitioning said physical layer device to a low power mode; andsubrating an interface between said physical layer device and a mediaaccess control device, said subrated interface reducing a power consumedby said interface.
 12. The method of claim 11, wherein saidtransitioning comprises lowering a link rate using a subset physicallayer device technique.
 13. The method of claim 11, wherein saidtransitioning comprises entering into a low power idle mode.
 14. Themethod of claim 11, wherein said subrating comprises reducing saidinterface to a zero rate.
 15. The method of claim 11, further comprisingturning off said interface.
 16. The method of claim 11, furthercomprising lowering a rate of said interface.
 17. The method of claim11, further comprising turning off one or more channels in saidinterface.
 18. The method of claim 11, further comprising reducing arate of one or more channels in said interface.
 19. The method of claim11, further comprising turning off lanes in a XAUI interface.
 20. Anenergy efficient Ethernet physical layer device that is coupled to amedia access control device, comprising: an interface for communicationwith the media access control device, said interface including one ormore channels; and a control module that transmits a control signal tothe media access control device over said interface indicating a needfor transitioning of said interface into a low power consumption mode,wherein said control signal indicates to the media access control devicea level of subrating on at least one of said one or more channels insaid interface.
 21. The device of claim 20, wherein said interfaceincludes a plurality of channels.
 22. The device of claim 20, whereincontrol signal is transmitted using in-band signaling.
 23. The device ofclaim 20, wherein control signal is transmitted using out-of-bandsignaling.
 24. The device of claim 20, wherein control signal istransmitted using register-based communication.
 25. The device of claim20, wherein said interface is a XAUI interface.
 26. The device of claim20, wherein said interface is a XFI interface.
 27. The device of claim20, wherein said interface is a xxMII interface.